1. Field of Invention
The present invention belongs to the field of micro-electronics technologies, specifically to a phase-change storage unit for replacing DRAM and FLASH and a manufacturing method thereof
2. Description of Related Arts
A phase-change memory uses an operating signal to generate Joule heat to operate a phase-change material, so that the phase-change material is transformed between different phases, thereby embodying the difference between high and low resistance values, so as to complete storage of information. The phase-change memory has a fast operating speed, a good data holding capability, and a strong cyclic operating capability, is compatible with the conventional CMOS process, and can still maintain the operating performance in a small size, so the phase-change memory is considered as one of the most promising next generation non-volatile memories. With the shrinkage of the device size, the influence of the size effect on the phase-change material is still the research focus of the phase-change memory at present.
The influence of the size effect on the heat stability of the phase-change material researched by researchers is frequently seen in reports. For example, the document (JOURNAL OF APPLIED PHYSICS 103, 114310 (2008)) once reported the change of the crystallization temperature of GeSb, Sb2Te, NGST, GST, and AIST with the change of the thin-film thickness. When the thin-film thickness of the phase-change material is above 10 nanometers, the crystallization temperature of the phase-change material changes very weakly with the change of the thickness. When the thin-film thickness of the phase-change material is below 10 nanometers, the crystallization temperature of the phase-change material is increased to different extents with the reduction of the thin-film thickness. For example, as the thickness of the thin-film is reduced from 10 nanometers to 2 nanometers, crystallization temperatures of Sb2Te, GeSb, GST, and AIST materials are respectively increased by almost 150, 50, 200, and 100° C.
The document (SCIENTIFIC REPORTS 2:360 DOI:10.1038/srep00360) reports that the size effect also influences the thin-film crystallization speed of the phase-change material simultaneously. When the thickness of the phase-change material is reduced, the specific surface area of the material is increased, and it is easy to form a crystal nucleus because defect exists at the interface. The existence of the crystal nucleus shortens the crystal nucleus forming time for the crystallization procedure of the phase-change material, thereby reducing the time required for the crystallization procedure, so as to improve the operating speed of the phase-change memory. When crystal nucleus forming time is shortened, crystalline grain growth becomes a principal factor of influencing the crystallization time. The crystalline grain growth time is shortened as the size is shrunk, so as to ensure a faster phase-change speed of a device in a small size.
A phase-change memory uses an operating signal to generate Joule heat to operate a phase-change material, so that the phase-change material is transformed between different phases, thereby embodying the difference between high and low resistance values, so as to complete storage of information. The effective part of the operating power consumption is energy of a part, of the phase-change material, which implements phase transformation. The smaller the phase-change region is, the smaller the required energy is, and the device power consumption is reduced. The phase-change memory in a limited structure reduces the device operating power consumption just by reducing the phase-change region. The preparation for an electrode in a small size such as a blade structure or ring-shaped structure also aims to reduce the phase-change region, thereby reducing the power consumption.
The principal failure reason of the phase-change memory is the material homogeneity reduction caused by element segregation of the phase-change material. The element diffusion principally occurs under a high-temperature condition generated by the current during the operation; the longer the high-temperature duration is, the more serious the element segregation is. Therefore, the long-time and high-power operation on the phase-change material facilitates the element segregation, thereby accelerating the device failure, and reducing the number of times at which the device may be cyclically operated. For the specific phase-change memory having low power consumption and fast operating speed, the operating time is short during operating, so the element segregation effect on the material is reduced at each time of operating, which is favorable to the improvement of the cyclic operating capability of the device.